Civil Engineering Reference
In-Depth Information
You should now have a chimney that is a perfect fit on the boiler barrel. This
method can be used for all sorts of fittings that need to be fitted to a specific
radius.
Trepaning
If you need to bore a hole in a relatively thin sheet of metal you can trepan the
centre out. Trepaning is a method of cutting a groove through a piece of metal
so the middle can be removed. The tool should cut on the bottom, and both
sides of the tool should be relieved. Feed the tool slowly through the metal
taking particular care when the centre breaks through. The hole can then be
finished using a conventional boring tool.
Boring outside diameters (turning)
You can bore outside diameters in the mill. This is the equivalent of turning.
You do this by putting a suitable tool in the boring head. If you have a left-
hand boring tool, use this, but if not, you can use a normal boring tool and run
the machine in reverse. This method is ideal if you want to machine a spigot
on an odd-shaped component and do not want the bother of setting it up in
the four-jaw chuck on the lathe. Start with the boring bar clearing the outside
diameter of the material and gradually reduce the boring head until the dia-
meter required is met.
REPETITION WORK
Machine stops
Machine stops are very useful especially if you do not have a digital readout.
Not all machines have table stops as standard, but they are not that difficult
to fit either. The mill's spindle will almost certainly have a depth stop to control
the depth of drilling.
If the milling machine has a knee that can be wound up and down, this is
the quick way to set the depth stop. Simply put the drill into the chuck or collet
and wind the spindle down to the stop; then wind the table up until the drill
touches the top of the work. Now we know where we are, we can raise the
